It's cause the bot don't have sufficient rights on the channel. Like a normal user it need some rights do be able to change channel topic. There is more indication about that there : https://github.com/md678685/justcord-3/issues/5#issuecomment-277989007
;-)

I've made something like this. Don't hesitate to extend it : https://github.com/zoski/jc3mp-iplogger
I use it to log my players IP, the final goal is to whitelist them during DDOS attack and drop unknown IP until the attack is over.
Edit : Markussr1984 did something more complete here